Soil drivers of NH3 emissions in a fertilized sunflower agroecosystem

: Ammonia (NH 3 ) volatilization represents a major pathway of reactive nitrogen loss in agroecosystems, yet the soil controls governing its variability remain insufficiently understood. In this study, we quantified soil-atmosphere NH 3 fluxes in a fertilized sunflower field in Hungary using multi-point field measurements (20 locations, 18 campaigns), combined with detailed soil, canopy, and microclimatic observations. To identify the dominant drivers of NH 3 flux variability, we applied a Random Forest modeling approach complemented by SHAP-based interpretation. The RF and SHAP analyses indicated non-linear, modelled associations of NH 3 flux with soil temperature, moisture, humus content, and the [NH 4 + ]/[H + ] proxy (Γ). Notably, properties measured in deeper soil layers (20–30 cm) contributed to the model predictions, indicating associations between NH 3 flux variability and vertically structured soil processes rather than surface conditions alone. NO 3 – emerged as a conditional, state-dependent model-associated indicator, potentially reflecting broader N-transformation dynamics and covariance with soil moisture and temperature rather than a direct causal effect on NH 3 volatilization. These findings emphasize that NH 3 fluxes arise from complex interactions among soil chemical status, microclimate, and nitrogen transformation processes within the soil profile. The results demonstrate that data-driven approaches can provide new insights into nitrogen cycling processes in agroecosystems.